Geoscience Reference
In-Depth Information
Cultivated southern slope
(sunny hillside)
North-facing slope given over to forest
(shaded hillside)
Highest level reached by the glacier
Broad-leaved trees
Conifers
Cultivated ledge
Steeply cut
rock
Moraine carpeting
the glacial valley
Alluvia often formed of recaptured
moraine material; at times
excessively wet
'U' shape of
the glacial
valley
Fig. 2.17
Cross-section of an Alpine valley with sides carpeted with moraines.
The particles transported by wind come from desert margins prone to
deflation because of lack of continuous plant cover.
In the interglacial period, hence the present time, the Sahelian borders
of the Sahara regularly provide Europe with reddish silts and clays that
fall from above during 'rains of blood'. They have been recorded in the
Bible. On the contrary, the Sahara proper, sandy and gravelly, has no
more silt to give!
In the cold period, ice rubs the boulders embedded in it against the
substrata. Thereby large quantities of pulverized minerals called glacial
flour are made (these materials can still be seen on high mountains, in
front of the present-day glaciers). This flour is transported by meltwater
until it reaches the glacio-fluvial fan where it dries out. It is then
easily transported by the wind. Thus the loessial cover is more or less
continuous in Europe and in Asia in front of the ice cap so that it was
most prominent in the Weichselian (Würm in the Alps). But another
origin is possible for the loess. During the cold periods, as the water
was immobilized in the form of ice, the sea level was lowered. Marine
sediments emerged along the coasts and in the estuaries. Not colonized
by vegetation, they added their contribution to the loess.
Aeolian silts
 
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